diff --git a/src/image.c b/src/image.c
index c81af45..0b23b20 100644
--- a/src/image.c
+++ b/src/image.c
@@ -300,7 +300,7 @@ void do_upload(char *filename){
         // Most packets will be `data_chunk_len`, but not the last one
         size_t actual_size = len - pos > data_chunk_len ? data_chunk_len : len - pos;
 
-        cbor_ensure_success(cbor_encode_byte_string(&map, &payload[pos], data_chunk_len));
+        cbor_ensure_success(cbor_encode_byte_string(&map, &payload[pos], actual_size));
 
         if (pos == 0) {
             cbor_ensure_success(cbor_encode_text_stringz(&map, "len"));